This invention relates to the production of a monatomic beam of a particular element and, more particularly, to the production of a monatomic beam of oxygen produced by photodetachment of electrons from oxygen ions in the presence of a magnetic field.
In certain test environments it is desirable to produce a beam of atoms of a particular element that are neutral in charge and in the ground state. One example of such a situation is in the research surrounding the provision of spacecraft in low earth orbit. In order to test the reaction of materials to be utilized in the space station, it is necessary to simulate the atmospheric conditions at a height of 200 to 600 kilometers, which is typical low earth orbit altitude. It has been found by previous experiments that the atmosphere at such an altitude is comprised of essentially neutral atomic oxygen with an equivalent flux of approximately 10.sup.15 atoms/cm.sup.2 /second due to the orbital velocity at that altitude, which corresponds to an energy of about 5 electron volts. Previous attempts to produce neutral atomic oxygen beams have produced either beams of the required energy but with low flux rates, or beams with the required flux rate but with low energy. In either case, the beams are impure and sometimes ionic.
Many problems have arisen in previous attempts to produce neutral atomic oxygen beams in the five to eight electron volt energy, and 10.sup.15 atoms/cm.sup.2 /second flux range. Past attempts have often been based on heating molecular gases to extremely high temperatures to obtain neutral atoms with high translational velocities in order to achieve energies of five electron volts. However, this procedure results in high percentages of ionized species and also a high percentage of undesired excited-state species, which are not present at low earth orbital altitudes and which will react differently than the neutral species that are present at such altitudes. The ionized species can be filtered out at the exit plane of the beam apparatus to leave only the neutral atoms. This, however, results in a severe loss of flux. Removing the undesired excited species is even more difficult and has been performed by quenching the excited states, using a proper mixture of inert foreign gases, such as argon or krypton. The quenching procedure, however, results in an impure beam and a loss of kinetic energy of the ground-state species.
Another problem of prior art devices is the spatial divergence of the atomic oxygen beam. A magnetic field parallel to the path of an electron or ion beam can be used to collimate that beam, and will impart a spiraling motion to the charged particles within the beam. When neutral atoms are formed from spiraling ions, these neutral particles will tend to spiral outward. The magnetic field, however, will be useless in limiting the motion of neutral particles. Thus, the resulting beam which contains neutral atoms will be subject to spatial divergence, which is often referred to as "beam blowup".
Although generation of a beam of atoms in the ground state has been discussed thus far, the ability to produce a beam of atoms in a selected excited state, as well as in the ground state, would be a useful characteristic of a monatomic beam generator, increasing the scope of scientific investigation for which the beam generator could be used.
It is, therefore, an object of the present invention to provide a method and apparatus to produce a beam of atomic oxygen of neutral charge in which substantially all of the atoms are at the ground state and to provide such a beam of energy and flux density that simulates the atmospheric conditions at low earth orbital altitudes.
It is another object of this invention to provide a method and apparatus for producing monatomic beams of other elements in which the atoms are at the ground state and are of a predetermined energy.
It is still another object of the invention to direct a monatomic beam of oxygen or other elements to the desired target or collection device in such a manner that spatial divergence of the beam is avoided or minimized.
It is still another object of the invention to selectively produce a beam of atoms in a desired excited state, as well as in the ground state.